A spindle device of a machine tool interchangeably holds a various tools, rotates at a high speed and receives a large machining load when a workpiece is machined. The machining load may result in wear of a tool fitting hole of the spindle, breakage of a collet and Belleville springs for clamping a tool and wear and tear of the bearings. In most cases, the breakdown of the spindle appears in the spindle itself, within the spindle or in the bearings.
When such breakdown or failure is fixed at the site where the machine tool is used, conduits for supplying a fluid and air pressure for the lubrication, cooling and cleaning and electric wirings to the motors and limit switches are removed. Then, the spindle device is disassembled to replace the spindle, the parts within the spindle or the bearings, thereafter the spindle device is reassembled. The repair work is extensive, requires expert knowledge and skill and involves a great deal of time.
As a first prior art, Japanese Unexamined Patent Publication (Kokai) No. 11-99403 describes a spindle device of which the spindle can be divided into front and rear spindle parts when the spindle is replaced, the bearings and a rear bearing housing are removed from the spindle. Then, the front and rear spindle parts are decoupled for the replacement of the front or rear spindle part, thereafter, the spindle device is reassembled.
As a second prior art, Japanese Unexamined Patent Publication (Kokai) No. 3-103102 describes a spindle supporting arrangement of a machine tool in which the spindle, a front bearing, a rotor of a built-in motor and a rear bearing are removed as a whole by sliding the outer surfaces of the outer races of the bearings relative to the inner surface of the housing. The spindle device is reassembled after the spindle or the bearings are replaced and assembled back outside of the housing.
As a third prior art, Japanese Unexamined Patent Publication (Kokai) No. 4-57608 describes a spindle device which includes a cartridge housing in which the spindle and bearings are incorporated in a housing. The cartridge housing can be attached to a spindle carriage to a various machine tools. Although this publication does not disclose a method of replacing the spindle at a site where the machine tool is used, it suggests a replacement of the spindle and bearings as a cartridge.
As a fourth prior art, Japanese Unexamined Patent Publication (Kokai) No. 3-142101 describes a built-in motor type headstock including a main bearing part and a motor part. The main bearing part can be commonly used and a various sizes of the motor part are interchangeably used according to the requested specification.
According to the first prior art, the spindle is divided into the two parts so that only one of the front and rear spindle parts can be economically replaced. However, the at the time of replacement, the works of disengaging a shrinkage fit at the joint between the front and rear spindle part, coupling a new spindle part by a shrinkage fit and/or coupling or decoupling the bearings or the rotor which are coupled to the spindle by an interference fit require expert knowledge and skill and a special facility and therefore, cannot be conducted at a site where the machine tool is used.
According to the second prior art, although the spindle can be replaced easier that the first prior art, the outer races of the bearings, directly affecting the rotational accuracy of the spindle, are detached from and attached to the housing. Therefore, the replacement work requires expert knowledge and skill. Further, after the replacement of the spindle, a test run is conducted to check whether or not the noise, the vibration and the heat generation are normal. Therefore, the downtime of the machine tool for the spindle replacement is relatively long.
According to the third prior art, the cost for the replacement is increased because the whole of the housing must be replaced. Further, the conduits, electric wires and covers must be detached and attached to allow the spindle replacement. Therefore, the amount of work and time for the replacement is increased.
According to the fourth prior art, the main bearing part on the headstock cannot be separated from the motor part, at the site where the machine tool is used, for the replacement of the spindle and the front and rear bearings as a whole. In particular, the rear bearings must be disassembled from the bearing case and therefore, the spindle replacement work is very difficult.